1. Field of the Invention
The present invention relates to a laminated body comprising an aqueous solution which becomes cloudy to scatter and block light due to the action of heat resulting from absorption of light when it is irradiated with sunlight. The invention can be applied to buildings and automobiles and the like which have windows in which only the surface directly irradiated with light selectively blocks light and prevents glare. In addition, it can also be combined with a heating element for use in indoor windows of partitions, doors, etc. equipped with electronic curtains.
2. Description of the Related Art
In recent years, achieving more comfortable and energy-saving windows through effective use of sunlight has been a desirable goal in consideration of environmental compatibility. Although heat-reflecting glass and heat-absorbing glass are actually employed in windows, their use against daylight rays causes a problem by cutting off natural rays during winter, cloudy days and rainy weather, while also greatly reducing the feeling of openness and comfort. Therefore, adjustable glass has been desired, to allow blockage of light by a reversible change.
The present inventor focused on the energy of sunlight which is irradiated onto windows and investigated possibilities of the presence or absence of this energy causing a reversible change between transparency and light scattering as a self-response of the window glass, to provide a more comfortable living space. The inventor noted that such a property of self-response is very attractive not only from the standpoint of blocking light only on the irradiated surface and providing an energy-saving effect, but also in terms of finish, maintenance, support costs, etc. From this standpoint, photochromic systems, thermochromic systems or thermotropic systems may be selected for study, but their functioning mechanisms are complicated and thermochromic and thermotropic systems which depend only on the action of heat which can be easily controlled by manually adjusting the temperature when necessary, are superior to photochromic systems which depend on the light wavelength. The sunlight reaching earth is in the range of 290 nm to 2140 nm, of which about 80% is in the visible to near infrared range of 400 nm to 1100 nm, and also to be considered is the fact that the visible light range is larger than the near infrared light range. Thus, controlling the visible light range not only has a screening effect, but is also important for energy-saving and glare reduction effects. The present invention utilizes increasing temperature of objects, caused by sunlight energy. A heating element may, of course, be added for artificial temperature control to create a light-scattering condition to block out light.
At the current time, materials used in thermochromic and thermotropic systems have inadequate characteristics and are still impractical. For thermochromic glass and thermotropic glass to become widely used, the following conditions must be satisfied.
1. The phase change between transparency and opacity must be reversible. PA1 2. The reversible change must be repeatable without phase separation. PA1 3. The temperature at which phase transition begins must be low. PA1 4. The glass must be durable. PA1 5. The materials must not be toxic or environmentally polluting.
The present inventor has focused on aqueous solutions which undergo phase transition from a colorless, transparent state to a cloudy light-scattering state upon a temperature increase in the aqueous solution, as a self-responding material capable of satisfying these conditions.
Solutions known to be altered to a cloudy light-scattering state by a temperature increase include non-ionic surfactants which exhibit the phenomenon of a clouding point but, although this application was also studied, it will be understood as obvious that phase separation readily occurred with increase in temperature and the above conditions 1 and 2 were not satisfied. Also, aqueous solutions of certain non-ionic water-soluble polymers (e.g. hydroxypropyl cellulose, poly-N-isopropylacrylamide, polyvinyl methyl ether, etc.), which undergo aggregation and gelation with rising temperature to exhibit a clouding and light-scattering effect were also studied for similar applications (Japanese Examined Utility Model Publication 41-19256, Japanese Unexamined Patent Publication No. 52-62502, Japanese Examined Patent Publication No. 61-7948), but they, too, failed to satisfy conditions 1 and 2 and were therefore impractical. Furthermore, applications of hydrogels have been attempted to utilize the change to cloudiness of hydrogels made of special reaction mixtures with at least 5 components, as described in Japanese Unexamined National Patent Publication No. 63-500042, but here as well, they cannot satisfy conditions 1 and 2 and are therefore impractical. Also studied have been crosslinking hydrogels such as poly-N,N'-methylenebisacrylamide gels obtained by aqueous solution polymerization of N-isopropylacrylamide in the presence of a water-soluble radical polymerization initiator, using a small amount of N,N'-methylenebisacrylamide as the crosslinking agent, but these also fail to satisfy conditions 1 and 2 and are therefore impractical. Thus, the present inventors have invented a useful laminated body based on a study of a new method and the finding that by utilizing the principle of sol-gel phase transition based on composition as described in Japanese Unexamined Patent Publication No. 6-255016, a non-ionic water-soluble polymer which undergoes aggregation to become cloudy and light-scattering is reversibly altered in a uniform manner without phase separation. The present inventor also carried out diligent research on the use of oily amphipathic substances with clouding points, which have been ignored so far, because of ready phase separation between the aqueous and oil layer in high temperature ranges. As a result, the present invention has been accomplished upon the discovery of an aqueous solution which uniformly undergoes a reversible change by sol-emulsion phase transition.